﻿44 



ON THE CLASSIFICATION OF BIRDS. 



GlireSy as also in pigs, anteaters, armadillos, moles, and 

 shrews, all which groups are of the gliriform type, corre- 

 sponding to the tenuirostral among the perchers. The 

 eyes are defended and protected by two sorts of eyelids ; 

 the first being those which are common to quadrupeds, 

 and which are external : these, in the generality of birds, 

 are clothed with small feathers, but are destitute of lashes: 

 sometimes they are surrounded with a fleshy, naked skin, 

 which is frequently so delicate as scarcely to be discerned, 

 as in some of the American trogons, but this sort of 

 ring in the turaccos (Corythaxoc 111.) is much broader, 

 and begins to form a prominent dentated rim, the full 

 development of which is seen in the genera Perspicilla 

 {fig. 11.) and Prionops. What function this very sin- 

 gular appendage is intended to perform, is altogether 

 unknown ; but it is more prevalent in tenuirostral types 

 than in any other ; and in the genus Zosterops it is re- 

 presented by a circle of thick, glossy, dense feathers, of a 

 snowy whiteness, which is more or less conspicuous in 

 every species. It is chiefly in the family of cuckows 

 ( Cuculidce), that we meet with eyebrows ; they consist 

 of a fringe, on the upper eyelid, of rigid, stiff bristles, 

 placed singly, and sometimes much developed; but at 

 all times they are sufficiently long to overreach the 

 ball of the eye. The genus Centropus, more especially, 

 is thus distinguished ; the same structure, less deve- 

 loped, may be seen in nearly all the CoccyzincB ; but in 

 the European cuckoo, and its immediate allies, these 

 eyelashes are entirely wanting. There can be no doubt 

 that this additional protection to the eyes is given to 

 birds whose habits lead them into close thickets, and 

 who explore dense foliage for their subsistence. We 

 know, at least, from personal observation, that such 

 are the haunts of all the South American CoccyzincB ; 

 and there is additional reason to believe in this con- 

 jecture, from the peculiar hardness and rigidity of the 

 feathers in Centropus (fig. 20.), the shafts of which 

 (a) are hard, glossy, and rigid, each ending in a point, 

 so that, but for their webs (b), they would become 



